An expansion device, such as an expansion valve, is required in a refrigeration system or HVAC system to control refrigerant flow and maintain an optimum gas condition of the refrigerant entering the suction side of the compressor. Electronic expansion valves (EXVs) are typically used in refrigeration and HVAC systems. An EXV is an electronically driven valve that is typically adjusted based on control algorithms utilizing sensed temperature and pressure values in the refrigeration system. For example, typical control of EXVs involves a controller sending a signal to open or close the valve based on an evaluation of suction gas superheat. Superheat is the difference between an actual refrigerant temperature and a saturated refrigerant temperature. An accurately controlled EXV allows refrigerant entering the evaporator to fully evaporate in the evaporator. If the refrigerant does not fully evaporate in the evaporator, liquid refrigerant may enter the compressor and cause damage or failure. Therefore, the superheat threshold in the suction line of the compressor is maintained at an optimum value to prevent compressor damage while still operating at the most efficient point possible.
Typically, the EXV must be controlled across a wide range of HVAC operating conditions, including, but not limited to, temperature, humidity, and load. Under certain conditions, such as low ambient temperature start conditions (i.e., cold start or cold soak), long line set applications, or other transient operational conditions, suction pressure of the compressor may be especially low and cause low pressure trips to occur. These conditions often occur during system startup and prevent reliable operation of the HVAC system.
Therefore, there remains a need for a system and method of controlling an electronic expansion valve to provide reliable operation of an HVAC system across all operating conditions.